Plural stage fluidization and vibration of cohesive plant material



May 12, 19.70

J. G. LEWIS' 3,511,843 PLURAL STAGE FLUIDIZATION AND VIBRATION OF COHESIVE PLANT MATERIAL Filed Oct. 13, 1966 United States Patent US. Cl. 260-291 4 Claims ABSTRACT OF THE DISCLOSURE A method of fluidising a cohesive material, e.g. ground damp tobacco, wherein the action of the fluidising gas is assisted by horizontal vibration of the material.

This invention relates to fluidised beds and in particular to the problem of maintaining a cohesive material in a fluidised state.

Cohesive material includes for example material which tends to cake, e.g. moist granular or powdered material and fibrous material in which the fibres tend to stick together. Included in this type of material is damp ground tobacco. Although not so restricted, the invention will hereinafter be described with reference to its use with damp ground tobacco. The problem encountered in attempting to fluidise such materials is that the gas, e.g. steam employed, simply blows holes through the material forming discrete passages without disturbing the remainder of the material.

According to one aspect of the present invention, a method of maintaining a cohesive material in a fluidised state comprises urging gas through the material and simultaneously mechanically agitating the material.

It has been found that the mechanical agitation, preferably in the form of continuous and regular shaking or vibration, prevents the occurence of the discrete passages for the gas, thus enabling the gas to completely fluidise the material.

In a preferred application, the method comprises passing gas vertically upwardly through the material and simultaneously mechanically agitating the material in a generally horizontal plane.

The method may be applied to counter flow arrangements in which case the material is caused to flow generally vertically downwardly in counterflow with the flow of gas.

Although the invention may be used generally for the extraction of volatile essences from plant material, or the recovery of solvents from plant material e.g. by steam distillation, the invention is particularly suitable for use in extracting nicotine from ground tobacco which has been treated with a suitable alkali by distilling the nicotine in a flow of steam. Although nicotine can be distilled in a steam passed over ground tobacco, much more rapid extraction of the nicotine can be achieved if the steam is blown through the ground tobacco which is maintained in a fluidised state. In accordance with the present invention, the ground tobacco can be maintained in the fluidised state by mechanically agitating the tobacco simultaneously with the passage of steam therethrough.

According to a further aspect of the present invention there is provided apparatus for maintaining a cohesive material in a fluidised state comprising a chamber for holding the material, means for urging gas through the material in the chamber and agitating means for agitating the chamber simultaneously with the gas flow therethrough.

The chamber may be substantially vertically disposed, the bottom substantially horizontal wall thereof being perforated to provide entry ports for the said gas.

In a preferred embodiment there are a plurality of said chambers arranged vertically in line, with said perforated bottom walls dividing one chamber from the next, flow passages being provided between adjacent chambers for the vertically downward flow therethrough of said material, in counter flow to said gas.

The invention is illustrated merely by way of example in the accompanying drawing which shows apparatus in accordance with the present invention.

Referring to the drawing there is shown a composite cylinder 10 comprising three chambers 11, 12 and 13 disposed vertically in line with one another. The chambers have bottom walls, 11a, 12a, 13a respectively which are apertured as shown to provide free flow of steam through the cylinder 10 from a steam inlet 14 at the bottom of cylinder 10 to a steam outlet 15 at the top of cylinder 10. The flow of steam is indicated by feathered arrows. Provided at the top of cylinder 10 is a material inlet 16 through which damp ground tobacco which has been treated with a suitable alkali is passed into the chamber 11. An overflow passage 17 is provided for conducting the overspill of ground tobacco from chamber 11 down to chamber 12. A further overflow passage 18 is provided for conducting the overspill of ground tobacco from chamber 12 to chamber 13. A third overflow passage 19 conducts the overspill of tobacco from chamber 13 to a material outlet 20 provided in the base of the cylinder 10. Thus the passage of ground tobacco through the cylinder 10 is indicated by plain arrows. To prevent condensation in the cylinder 10 the said cylinder may be fitted with a steam jacket, not shown.

In operation, the cylinder 10 is filled with tobacco to the condition shown in the figure, whereby tobacco fills each of the chambers 11, 12, 13 up the level of its respective overflow channel. Steam is then pumped vertically upwardly through the cylinder 10 to pass through the tobacco in each of the chambers 11 to 13. Arms 21, 22, 23, 24 pivotally attached to the outer surface of cylinder 10 are then caused to continuously vibrate the cylinder 10 in a substantially horizontal plane by drives from suitable eccentrics. Alternatively the cylinder 10 may be freely suspended and agitated by out of balance weights rotating on vertical shafts carried in bearings attached to the cylinder 10.

The action of agitating the tobacco within chambers 11, 12 and 13 prevents the steam from blowing discrete holes in the tobacco and, together with the flow of steam through the tobacco, results in fluidisation of the tobacco within the chambers 11, 12 and 13. Further ground tobacco is urged into the cylinder 10 through entrance 16 and so a continuous flow of tobacco is provided through the cylinder 10 in a vertically downward direction in counter-flow to the generally upward flow of steam.

The steam leaving outlet 15 contains nicotine which can then be recovered or concentrated by various known means.

It will be noted from the figure that the overflow channels 17 and 18 are open-ended and dip below the level of the ground tobacco in the lower chamber. This is necessary to prevent the steam from entering these channels and thus flowing into the next chamber by passing the apertured bottom walls 11a, 12a, and thus not fluidising the tobacco. The channels 17 and 18 can be redesigned so that they do not dip below the level of the tobacco in the lower chamber provided the lower outlet from these channels is provided with a suitable one-way valve, e.g. a flexible flap valve which is operated by the weight of ground tobacco falling upon it but which is closed by the pressure of steam acting on it. In this way ground tobacco is passed from upper to lower chambers but steam is prevented from passing through these channels from lower to upper chambers.

Although the invention has been described with reference to its use in extracting nicotine from tobacco, it will be appreciated that the apparatus may be used for extracting volatile essences from other plant materials or to the recovery of solvents from plant materials by steam distillation for example. Other mass transfer processes involving cohesive material may also employ the present invention to advantage, since these materials may be rendered fluidised by the use of mechanical agitation together with the suitable gas flow through the material.

What is claimed is:

1. A method of contacting particles of a cohesive plant material with a gas which comprises the steps of: introducing particles of a cohesive plant material into a first fluidizing chamber; introducing a gas upwardly from a further chamber located below said first chamber through said first chamber to form a fluidized bed of the cohesive plant material in said first chamber and simultaneously subjecting said first chamber to mechanical agitation in a horizontal plane only to subject the particles of cohesive material in said first chamber to horizontal agitation; removing said gas from the first chamber; continuously transferring a portion of the fluidized material from the upper portion of the fluidized bed of cohesive plant material in said first chamber sequentially to at least one further fiuidizing chamber located beneath said first chamber; introducing a gas sequentially upwardly through each of said further chambers from the lowermost chamber to said first chamber to form a fluidized bed in each chamber of cohesive plant material transferred thereto from the adjacent chamber located thereabove to contact the particles with the gas and simultaneously subjecting each said further chamber to mechanical agitation in a horizontal plane only to subject the particles of cohesive material in said further chamber to horizontal agitation; and withdrawing the cohesive material from the lowermost chamber.

' 2. A method according to claim 1 wherein said plant material comprises damp ground tobacco.

3. A method according to claim 1 wherein said gas comprises steam.

4.' A method according to claim 1 wherein said plant material comprises alkali treated ground tobacco and said gas comprises steam, said steam removing nicotine from said tobacco by distillation.

References Cited UNITED STATES PATENTS 1,083,802 1/1914 Castona 202-234 1,127,452 2/1915 Koch 202- 2,246,914 6/1941 Craggs' 34-164 2,813,823 11/1957 Putman 203-97 2,876,557 3/ 1959 Ducatteau 34l64 3,043,752 7/1962 Foch 201-31 3,058,235 10/1962 Morris et al 34-164 3,161,483 12/1964 Morris 34-57 3,284,317 11/1966 Jahnig et a1. 201-31 3,288,878 11/ 1966 Hachmuth.

2,478,473 8/ 1949 Eskew 260-291 WILBUR L. BASCOMB, IR., Primary Examiner US. Cl. X.R. 

